Current practices related to coal processing for heat and energy production perform at varying levels of efficiency and also produce unacceptable levels of noxious exhaust emissions. Efficiency levels can be adversely affected according to coal grade availability and unacceptable emissions from any coal grade include nitrogen oxides, sulfur oxides, gaseous mercury, soot and high levels of variously contaminated carbon dioxide.
The combination of these various inefficiencies associated with current coal industry practices has created such extreme conditions that many coal processing facilities have been forced to cease operating, a situation that has created many downstream negative affects including severe loss of industry revenue, loss of employment opportunities in not only coal processing industries but also mining operations, as well as an overall reduction in available energy resources both domestically and internationally. All of this occurring at a time when the combustion of raw coal to generate electricity is especially needed to supply the increasing demands of the global economy.
Another use for raw coal is the production of liquid hydrocarbon fuels using the Fischer-Tropsch coal-to-liquid fuel (“FTCTL”) process, by which coal is converted from its raw state into liquid forms by breaking down the coal to a first product building block (carbon monoxide) through partial combustion in a low-oxygen atmosphere, followed by a series of catalytic reactions to convert the carbon monoxide with hydrogen to liquid hydrocarbons. The FTCTL process, however, is also only variously efficient depending on available coal grades and is known to produce unacceptable levels of exhaust emissions that include nitrogen oxides, sulfur oxides, gaseous mercury, soot, fine and less fine particulate matter, and high levels of variously contaminated carbon dioxide.
Current methods for coal processing have varying levels of heat efficiency produced by differing grades of mined coal. While anthracite and bituminous coal are now preferred as heat-producing feedstocks, lignite reserves are currently mined to a limited extent because heat value versus waste (solid, liquid and gaseous) is not sufficient to justify full-scale mining and use of lignite coal for heat and power generation.
A problem associated with current methods for coal processing is the industry's inability to make use of other feedstocks which could significantly increase the energy production yield from existing coal processing facilities. Other carbon-based feedstocks which could provide very high heat efficiency for energy production include landwaste, seawaste, industrial waste, plastics waste and petroleum coke (“pet coke”). Current practices in which raw feedstocks are combusted produce unacceptable levels of exhaust pollutants such as nitrogen oxides, sulfur oxides, gaseous mercury, soot, fine and less fine particulate matter, and variously contaminated carbon dioxide, which all require very expensive and variously insufficient post-combustion exhaust stream scrubbing and prohibitively expensive removal of other waste streams. Another problem associated with the possible use of land, sea, industrial, plastic waste and pet coke are the widely varying levels of heat available from the burning of these materials in their raw state.
Current methods for coal processing also have unpredictable levels of contamination of the final exhaust product, carbon dioxide. Even with current exhaust scrubbing mechanisms, contamination levels are often unacceptably high (especially nitrogen oxide levels) as is the expense associated with soot accumulation in scrubbing and/or catalytic conversion mechanisms.
While there are potential uses for carbon dioxide which include sequestering and recently discovered methods for recirculating to produce liquid hydrocarbon fuel, any level of contamination in the final carbon dioxide exhaust stream impedes its reactivity level and resulting efficient use.
Yet another efficiency problem associated with current coal processes is the very low extraction rate of rare earth elements such as scandium, yttrium, lanthanum and cerium from slag and ash residue left following coal combustion. Current methods for extraction, at their very best, result in only about 2% extraction rate of rare earth elements from coal-derived ash and slag. Because there are important uses for these elements in the health care, transportation and electronics industries as well as military use, inefficient extraction processes involving ash and slag is a missed opportunity.
Prior art developments intended to improve coal process efficiency levels include fuel cell technologies designed to augment heat value from coal processes without increasing exhaust and waste streams. Post-combustion scrubbing technologies are continually being developed to improve scrubbing efficiency, especially pertaining to soot trapping and removal of excess soot from scrubbing and catalytic converter mechanisms. Coal gasification is another method intended to improve efficiency levels of heat production from coal while reducing exhaust pollutants. Other prior art methods for improving coal process efficiency involve developments in surfactant technologies which are used to extract rare earth elements from coal-derived post-combustion slag and ash.
Two prior art systems are described in U.S. Pat. Nos. 8,822,553 and 9,334,796 in which coal in the first patent, or any carbon-based material in the second patent, are converted to fuel through processes that first produce heat (and electricity according to the second patent) and carbon dioxide (CO2). The carbon dioxide is then recirculated and reacted with carbon black or coke (C) to produce carbon monoxide (CO). The carbon monoxide resulting from the reaction of carbon dioxide and carbon black is then further reacted with hydrogen (H2) produced by or from several possible reactions or sources to form liquid hydrocarbon fuel according to FTCTL practices.
Thus, the prior art describes systems by which coal or a carbon-based material can be used to produce fuel by first generating heat (and electricity) and carbon dioxide from the coal or carbon-based material and recirculating the carbon dioxide to react with carbon black to form carbon monoxide, which is then reacted with hydrogen to form liquid hydrocarbon fuels. These systems address the problem of excessive carbon dioxide emissions from the combustion of coal or a carbon-based material by converting the coal or carbon-based materials to fuel. While these processes address the problem of carbon dioxide exhaust as an undesirable final product from coal or carbon-based material processing, they are specifically linked to carbon dioxide recirculation and fuels production and do not address the many other problems associated with current coal processing methods described above.